共查询到19条相似文献，搜索用时 140 毫秒
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本文详细地介绍了利用二维离散付里叶变换(DFT)进行图象复原的方法。文中给出了一种利用频谱拟合来准确地求得系统的光学传递函数的方法。在云台CCD系统上进行实际试验的结果表明将系统的空间分辨率提高了2.75倍,将原来连在一起的双星明显地分开了。最后,文章还对DFT图象复原的优缺点进行了讨论。 相似文献
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根据在射电天文频谱观测中出现的新需求,介绍了近年来数字技术的新进展.达到GHz采样速率的多位高速模数转换器(Analog-to-Digital Converter,ADC)、海量数字处理芯片现场可编程门阵列(Field Progxammable Gate Array,FPGA)以及运行在这些芯片上的并行快速傅里叶变换知识产权(Fast Fourier,Transform Intellectual Property,FFT IP)内核,结合高性能数据总线的系统集成,为射电天文构建新型FFT频谱仪提供了可能的技术选择.与现有其他类型频谱仪相比,集成了这些新技术的数字型FFT频谱仪有更大的带宽、更高的谱分辨率、更高的动态范围和整体稳定性,此类频谱仪的出现显示了射电频谱技术已经进入了新一代数字技术应用的阶段. 相似文献
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为完成对太阳射电爆发15 MHz～15 GHz频谱的监测,云南天文台研发4套太阳射电频谱仪,频率覆盖范围依次为15～80 MHz, 100～750 MHz, 600～4 200 MHz和4～15 GHz,分别称为十米波、米波、分米波和厘米波太阳射电频谱仪。十米波段太阳射电频谱仪的谱分辨率和时间分辨率分别为7.6 kHz和1 ms;米波段和分米波段太阳射电频谱仪的谱分辨率和时间分辨率分别为9.5 kHz和10 ms;厘米波段太阳射电频谱仪的谱分辨率和时间分辨率分别为76 kHz和10 ms。每套设备包括天线系统、接收机和数字频谱仪。为实现超高谱分辨率,需要的快速傅里叶变换(Fast Fourier Transform, FFT)点数最高达到262 144,在现场可编程门阵列(Field Programmable Gate Array, FPGA)上,通过一个FFT IP核(Intellectual Property Core)不能实现如此高点数的快速傅里叶变换运算。对于大点数的快速傅里叶变换,需要对数据行列分解后做并行处理,从而将其转化为两个小点数的快速傅里叶变换。通过对并行算法的研究,... 相似文献
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本文研究太阳从可见光至近红外连续谱中的五分钟振荡。介绍采用连续谱观测的原理,并分析观测结果。在从连续谱的时间序列中消除了仪器响应轮廓及地球大气效应后,由快速付上叶变换(FFT)得出的功率谱。从研究功率叠加及位相相互关系中查找出低l的五分钟振荡模式。最后,在文章后的附录中讨论了大气的红外吸收窗口问题。 相似文献
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《天文学进展》2016,(2)
我国正在建设500m口径球面射电望远镜(FAST),为了能够充分发挥自身口径大的优势,确保望远镜在世界上的领先,将自主研发世界一流的超宽带通用型数字后端(CRANE)。在整个CRANE开发中,硬件部分通过与中科院自动化研究所的合作,不仅开发了现场可编程门阵列(FPGA)运算板FDB(FAST Digital Backend),还开发了3 Gbits/s 12 bits的宽带高精度模数转换电路板(ADC)芯片,并用此实现3 GHz带宽的一次性覆盖。此超宽带通用型数字后端同时也包括开发模拟信号前端电路板(AFB)。固件部分,目前研制者计划在FDB上实现百万级通道频谱仪——CRANE项目将优化FFT,研究级联式FFT来实现大点数FFT。一级FFT运算单元的分辨率可能会造成最终频点输出时信号失真,通过在Matlab上进行级联FFT算法仿真,研究了信号失真的情况,并用Matlab模拟还原出真实信号。 相似文献
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本文提出了利用计算机对线性系统的模糊进行复原的原理和方法。指出在离散格点上实现复原的可能性。线性系统的输入和输出由一个卷积关系互相联系。任何对实际系统的测量结果都得到一个离散的序列,因此可以用解线性代数方程组的方法或用离散付里叶变换(DFT)的方法来复原被系统模糊了的输入。文章在对复原过程的误差影响进行了定性分析之后,给出了一个关于复原的分辨率的判据,使我们对于复原结果的可靠性有一个较严格的标准。 相似文献
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针对传统FFT捕获算法运算量较大的缺点,利用时域载波剥离与频域圆周移位等价的原理,通过对输入信号频谱序列进行圆周移位操作,替换在不同载波Doppler搜索单元下对输入信号的重复载波剥离和FFT操作,在Doppler单元和码相位的二维搜索过程中,只需对输入信号进行一次FFT操作.该算法不会给相关能量带来损失,因此,该算法不会影响信号的捕获概率.实验结果证明该算法具有捕获时间短,相应硬件实现简单等优点,适合GPS软件接收机的工程实现. 相似文献
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快速傅里叶变换(Fast Fourier Transform,FFT)比傅里叶变换有更好的算法性能,是射电干涉成像的基础算法,但因为天线阵列的不规则采样,需使用网格化算法将可见度数据重采样到规则的网格上才能应用。基于卷积的网格化计算具有密集型和迭代型的特点,特别是处理海量可见度数据的情况下,高性能的网格化计算对整个成像过程加速尤为重要。为了缓解数据处理的压力,在现有处理整块数据和支持多核计算的算法基础上,拓展应用Dask并行计算框架,不仅将数据分块并分配到多线程上,提高数值计算效率,而且动态的分布式任务调度策略优化了网格化的实时处理。实验结果表明,多核中央处理器利用率显著提高,即使增加数据量,也能进一步提高网格化算法的性能。分布式任务调度能够将单(多)测量集的网格化弹性缩放到单(多)机系统,充分发挥集群的规模化优势。 相似文献
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Short-term periodicities of solar activity were studied with the flare index by using Discrete Fourier Transform for the time interval 1966–1986. Two noticeable periodicities (18.5 and 5 months) have been found. The existence of these periodicities comparing with the early findings is discussed. 相似文献
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Atila Özgüç 《Astrophysics and Space Science》1989,162(1):123-127
In the present paper, the time series of 1–8 Å X-ray index for the time interval between January 1977 to September 1981 has been analyzed by carrying out power spectrum using Discrete Fourier Transform. The 78-day periodicity which is one-half of the period found from various solar parameters of cycles 20 and 21 by various authors, was found. This periodicity is thought to be related to the 152-day periodicity. 相似文献
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The aim of the present study is to investigate the short-term periodicity in the solar radius measurements and to compare
with the short periods in sunspot numbers, sunspot areas and flare index data. The spectral analysis of data sets covering
a time interval from 26 February 2000 to 26 October 2007 during Solar Cycle 23 were made by using the Date Compensated Discrete
Fourier Transform (DCDFT). The power spectrum of solar radius data corrected for the seeing effect gives an evident peak at
25.7 days with the amplitude of 0.034 arcsec, which is slightly different from the peaks of 26.2 and 26.7 days produced by
sunspot numbers and sunspot areas data, respectively. Besides, the main peak of 25.7 days detected in the power spectrum of
solar radius data is in agreement with the period of 25.5 days, suggested to be the fundamental period of the Sun by Bai and
Sturrock (in Nature
350, 141, 1991). 相似文献
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In the paper two chosen features of the comet 103P/Hartley 2 are studied. The first one are ‘cometary geysers’ which have been recorded by the camera on Deep Impact spacecraft. The numerical calculations related with this phenomenon have been carried out for large number of values of probable cometary characteristics. Our calculations confirm the assumption what also has been observed by NASA's scientists that the jets of carbon dioxide from the geysers are able to lift large chunks of water ice from the comet. The second discussed feature of the comet 103P/Hartley 2 is the lack of impact holes on the surface of its nucleus. The expected rate of impact holes on the surface of the nucleus of 103P/Hartley 2 is discussed. These holes could be the product of impacts between this comet and other small bodies orbiting in the main asteroid belt. The probability of such impacts, the total number of expected perceptible holes and changes in the luminosity of the comet caused by collisions are examined. We conclude that indeed the number of visible holes on its surface should be negligible (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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H. Kiliç 《Solar physics》2009,255(1):155-162
The short-term periodicities in sunspot numbers, sunspot areas, and flare index data are investigated in detail using the
Date Compensated Discrete Fourier Transform (DCDFT) for the full disk of the Sun separately over the rising, the maximum,
and the declining portions of solar cycle 23 (1996 – 2006). While sunspot numbers and areas show several significant periodicities
in a wide range between 23.1 and 36.4 days, the flare index data do not exhibit any significant periodicity. The earlier conclusion
of Pap, Tobiska, and Bouwer (1990, Solar Phys.
129, 165) and Kane (2003, J. Atmos. Solar-Terr. Phys.
65, 1169), that the 27-day periodicity is more pronounced in the declining portion of a solar cycle than in the rising and maximum
ones, seems to be true for sunspot numbers and sunspot area data analyzed here during solar cycle 23. 相似文献
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L. V. Ksanfomality 《Solar System Research》2011,45(6):504-514
Cometary nuclei are being actively studied using spacecrafts. In November 2010, the Deep Impact spacecraft (EPOXI project, NASA) approached the nucleus of comet 103P/Hartley 2 and returned images of this small celestial body having a dumbbell shape with a smooth neck. Since rotation of the nucleus leads to centrifugal forces, it is assumed that the dumbbell neck appeared as the result of their effect and the neck is lengthening slowly but continuously, which should eventually result in fragmentation of the nucleus. This paper considers dynamical evolution of the nucleus of comet Hartley 2. Calculations show that centrifugal forces exceed gravitational forces in the narrow part, and the nucleus can indeed undergo upcoming breakup and fragmentation into two parts. If there are no external perturbations, both parts of the celestial body will drift apart to a distance of less than 1 km from each other. The nucleus of comet Hartley 2 is an observed example of breakup of a celestial body. Asteroid Itokawa is considered, which has a similar feature but does not seem to undergo breakup. 相似文献
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Roy Soumya Prasad Amrita Panja Subhash Chandra Ghosh Koushik Patra Sankar Narayan 《Solar System Research》2019,53(3):224-232
The radio frequency emission at 10.7 cm (or 2800 MHz) wavelength (considered as solar flux density) out of different possible wavelengths is usually selected to identify periodicities because of its high correlation with solar extreme ultraviolet radiation as well as its complete and long observational record other than sunspot related indices. The solar radio flux at 10.7 cm wavelength plays a very valuable role for forecasting the space weather because it is originated from lower corona and chromospheres region of the Sun. Also, solar radio flux is a magnificent indicator of major solar activity. Here in the present work the solar radio flux data from 1965 to 2014 observed at the Domimion Radio Astrophysical Observatory in Penticton, British Columbiahas been processed using Date Compensated Discrete Fourier Transform (DCDFT) to identify predominant periods within the data along with their confidence levels. Also, the multi-taper method (MTM) for periodicity analysis is used to validate the observed periods. Present investigation exhibits multiperiodicity of the time series F10.7 solar radio flux data around 27, 57, 78, 127, 157, 4096 days etc. The observed periods are also compared with the periods of MgII Index data using same algorithm as MgII Index data has 99.9% correlation with F10.7 Solar Radio Flux data. It can be observed that the MgII index data exhibits similar periodicities with very high confidence levels.Present investigation also clearly indicates that the computed results are very much confining with the results obtained in different communication for the similar data of 10.7 cm Solar Radio Flux as well as for the other solar activities.
相似文献18.
In this study, we look for the mid‐term variations in the daily average data of solar radius measurements made at the Solar Astrolabe Station of TUBITAK National Observatory (TUG) during solar cycle 23 for a time interval from 2000 February 26 to 2006 November 15. Due to the weather conditions and seasonal effect dependent on the latitude, the data series has the temporal gaps. For spectral analysis of the data series, thus, we use the Date Compensated Discrete Fourier Transform (DCDFT) and the CLEANest algorithm, which are powerful methods for irregularly spaced data. The CLEANest spectra of the solar radius data exhibit several significant mid‐term periodicities at 393.2, 338.9, 206.5, 195.2, 172.3 and 125.4 days which are consistent with periods detected in several solar time series by several authors during different solar cycles. The knowledge relating to the origin of solar radius variations is not yet present. To see whether these variations will repeat in next cycles and to understand how the amplitudes of such variations change with different phases of the solar cycles, we need more systematic efforts and the long‐term homogeneous data. Since most of the periodicities detected in the present study are frequently seen in solar activity indicators, it is thought that the physical mechanisms driving the periodicities of solar activity may also be effective in solar radius variations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Based on a search for multi‐periodic variability among the semi‐regular red variable stars in the database of the All Sky Automated Survey (ASAS), a sample of 72 typical examples is presented. Their period analysis was performed using the Discrete Fourier Transform. In 41 stars we identified two significant periods each, simultaneously present, while the remaining 31 cases revealed even three such periods per star. They occur in a range roughly between 50 and 3000 days. Inter‐relationships between these periods were analyzed using the “double period diagram” which compares adjacent periods, and the so‐called “Petersen diagram”, the period ratio vs. the shorter period. In both diagrams we could identify six sequences of accumulation of the period values. For five of these sequences (containing 97 % of all data points) we found an almost perfect coincidence with those of previous studies which were based on very different samples of semiregular red variables. Therefore, existence and locations of these sequences in the diagrams seem to be universal features, which appear in any data set of semi‐regularly variable red giants of the AGB; we conclude that they are caused by different pulsation modes as the typical and consistent properties of similar stellar AGB configurations. Stellar pulsations can be considered as the principal cause of the observed periodic variability of these stars, and not binary, rotation of a spotted surface or other possible reasons suggested in the literature. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献